DIY Doctor

Fusebox requirements for new Regs in July?

Postby D-Mac » Sat May 24, 2008 3:16 pm

Hello all,

I have to fit a new fusebox in my house and having spoken to an Electrician friend I have been advised to install one with an RCBO on every circuit as these offer greater protection over the MCBs and the new regs coming into force in July require such a setup.

Can I get a second opinion please as having looked at the cost of RCBOs, this fusebox is going to be massively expensive compared to split load boxes.

Also, is anybody aware of a supplier selling complete RCBO fuseboxes or do I need to purchase every component separately (empty fusebox and individual RCBOs)?

Thank you.
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Postby ericmark » Sun May 25, 2008 12:36 am

Local supplier to me is Chester was selling RCBO's at £12.50 each and there seems to be a consensus among manufactures that if you use a board with two RCD's this will comply Screwfix offer two fully populated boards at £137 and £112 both Wylex 10 way. Either way not that much difference in price and all RCBO's is less likely to cause problems with tripping.

Postby D-Mac » Mon May 26, 2008 8:51 am

Thanks EricMark,

The boards that you suggested at Screwfix appear to have a mix of RCDs and MCBs. I have found similar boards at B&Q for approx £60-70. What I was looking for was a board completely full of RCBOs instead of the usual MCBs. I thought about buying a blank board and buying the parts individually but as Screwfix are selling RCBOs at £40 I was put off - that makes the whole board cost £400-500!!!!!! Could you provide me with details of your local supplier please. £12.50 is an excellent price.

I'm concerned that if I bought something now that the manufacturers are claiming will be adequate for the new regs, will I find that come July, my board is actually not acceptable?
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Postby ericmark » Mon May 26, 2008 4:10 pm

Think they are called Chester Electrical Ltd but main shop Oswestry Electrical and Plumbing Factors Ltd.
I am sure if they do them at £12.5 there must be other shops doing the same.
Can't remember the make was not one that roles of the tongue as well known.
I agree with you I am not sure if two RCD's really comply with what the BS7671:2008 says but I am sure if most the manufactures see it that way even if its not quite right it will be accepted like using blue as a core on 110 volt cable we all know it should be Brown and Black but everyone uses Brown and Blue and one is considered as being pedantic if you point it out.

Postby sparx » Mon May 26, 2008 8:43 pm

Hi, the regs only say that it is required to minimise the total loss of all lights and power if an rcd trips, so in fact a single isolator feeding two rcd's with circuits spread over the 2 fully meets requirements. RCBO's...pain in the a#$e as difficult to get 2 cores in each term for rings, all those extra earth flexes!!!
I have been accumulating 100 main switch isolators removed when changing for RCD's. Bought some cheap 2mod covers & wherever space allows intend to fit tails to isolator then 2 sets of tails to 2 small RCD boards, now being sold off cheap, low client cost, lots of room in boards, fully legal!
keep your options open I say,
regards SPARX
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Postby ericmark » Tue May 27, 2008 9:42 am

Multi-RCD’s are required to comply with:-
314.1 Every installation shall be divided into circuits etc. (only showing part of reg)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.
531.2.4 An RCD shall be so selected and the electrical circuits so subdivided that any protective conductor current which may he expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.

As I read it unless emergency lighting is used then lights should have there own RCD and not shared with any other circuit. The same would apply to fire alarm systems. Items like cookers which could cause other circuits to trip due to high earth leakage and sockets, likely used outside, should not really be on the same RCD as other items in the house. This could also apply to computer supplies.

Each house would have to be considered on its own as merit, with items like street lights which in the case of an RCD trip would afford enough light to safely exit. Also type of cooker fitted, with some not suffering from hydroscopic problems, which would include most ceramic hobs. But of course as with any health and safety items the reasons must be written down.

This brings us to the big problem which is Part P which requires the paper work to be sent either direct or through clearing agents to building control. The clearing agents are in the main not a problem as they use common sense and are from electrical back grounds but where dealing direct with building controls they are often not electrical people and very nervous about making mistakes and can be really pedantic in the way they read the regulations. And this will vary county to county.

But where manufactures recommend a method regulation 134.1.1 comes into play with:- Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.

As if this should over ride regulations like “531.2.8 Where an RCD is used for fault protection with, but separately from, an overcurrent protective device, it shall be verified that the residual current operated device is capable of withstanding, without damage, the thermal and mechanical stresses to which it is likely to be subjected in the case of a fault occurring on the load side of the point at which it is installed.â€

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